1. Field of the Invention
The present invention relates to a signal processing device for changing a resolution of a synthesized image signal obtained by synthesizing two image signals. Also, the present invention relates to an image output device outputting a plurality of synthesized image signals with different resolutions, by using such a signal processing device.
2. Description of Related Art
A conventionally known image output device is constituted so as to simultaneously output a plurality of synthesized image signals with different resolutions, by synthesizing a first image signal as a character signal such as an OSD signal for performing OSD (On Screen Display) display of channel information, time information, and menu, etc, and a second image signal as an original image signal. As an example, such a conventional image output device includes a first character signal creating unit for creating a first character signal with first resolution (such as 1920×1080 pixels); a second character signal creating unit for creating a second character signal with second resolution (such as 720×480 pixels); a first synthesizing unit for synthesizing the first character signal into the image signal with first resolution; a second synthesizing unit for synthesizing the second character signal into the image signal with second resolution; a first output unit for outputting a signal synthesized by the first synthesizing unit; and a second output unit for outputting a signal synthesized by the second synthesizing unit. Then, such a conventional image output device is adapted to create two character signals with different resolutions respectively in the first character signal creating unit and the second character signal creating unit, and synthesize these character signals with the image signal with each resolution, in the first synthesizing unit and the second synthesizing unit.
However, in the aforementioned conventional image output device, a plurality of character signal creating units (the first character signal creating unit and the second character signal creating unit) are required, for every resolution to create the character signal, and also a plurality of synthesizing units (the first synthesizing unit and the second synthesizing unit) for synthesizing the character signal with each resolution are required. Accordingly, there is a problem that the device is upsized and a cost is increased.
Therefore, the image output device is proposed, including the character signal creating unit for creating the character signal with first resolution; the synthesizing unit for synthesizing the character signal into the image signal with first resolution; the first output unit for outputting the synthesized image signal with first resolution synthesized by this synthesizing unit; a resolution changing unit for changing the resolution of the synthesized image signal with first resolution synthesized by the aforementioned synthesizing unit to the second resolution; and the second output unit for outputting the synthesized image signal with second resolution, with the resolution changed by the resolution changing unit, wherein the character signal and the image signal both having the same resolution are synthesized and the synthesized image signal is created, and thereafter the resolution of the synthesized image signal is changed.
For example, Japanese Patent Application Laid-Open No. H10-20847 discloses the image processing device wherein regarding the pixel at a specific position, a constituent pixel of an input image is used as it is, and regarding the pixel at a position other than the specific position, a pixel value is calculated based on the pixel value of the constituent pixel of the input image, and both pixels are synthesized to create the output image. More specifically, this image processing device includes calculating means for determining the pixel value of the pixel at the position other than the specific position, by multiplying the pixel value of the constituent pixel of the input image by a conversion coefficient expressed by a sum of power of 2; and output image creating means for creating the output image by synthesizing the pixel at the specific position (the constituent pixel of the input image as it is) and the pixel at the position other than the specific position with the pixel value determined by the calculating means.
According to a technique disclosed in the aforementioned Japanese Patent Application Laid-Open No. H10-20847, the conversion coefficient expressed by the sum of power of 2 is used. Therefore, by the changeover of the conversion coefficient, sharpness of the output image can be easily switched, and also the aforementioned calculating means can be constituted by a simple hardware such as shift resister, thus making it possible to reduce a manufacturing cost.
However, according to a technique disclosed in Japanese Patent Application Laid-Open No. H10-20847, during processing of changing the resolution of the image signal obtained by synthesizing a character signal such as an OSD signal, the resolution of the character signal is also changed. Therefore, the character signal and the image signal are mixed, thus involving a problem of bleeding in the image of the character signal.